For operation of a mobile radio network it is known to use a so-called home location register (HLR) in order to reach and to localize the terminals of mobile radio subscribers in the mobile radio network. The home location register is a central database that is an essential component of a mobile radio network. The mobile radio terminals are stored with the associated phone numbers (MSISDN, mobile subscriber ISDN), their status, that is to say whether or not they are registered in the mobile radio network, and their current location. In order to set up a communication link between a first mobile radio terminal and a second mobile radio terminal, the home location register is first of all checked to determine whether the second mobile radio terminal is registered in the mobile radio network. If this is the case, the register determines the cell in which the subscriber to be called is located, that is to say where it is registered, and the call is routed to the respective radio cell of the mobile radio network. The terminal is then reached, and can accept the call.
This technology that is currently used by the mobile radio operators, leads to an extremely large central database that manages the network-related user data of all subscribers in the mobile telecommunications network. This database is associated with a temporary buffer store, the so-called visitor location register (VLR) that is located in a mobile switching center (MSC) of a cell, and in which user data are stored for those mobile radio terminals that are currently located in the geographic coverage area of that switching center. The home location register and the visitor location register furthermore contain user's main data, by means of which authorization verifications can be obtained for authentication purposes. Further information relating to the home location register and the visitor location register is defined in international Standards, as specified by the European Telecommunications Standards Institute (ETSI) or the 3rd Generation Partnership Project (3GPP).
The so-called home subscriber service (HSS) represents a further development of the home location register (HLR). This is a database that is used for authentication and authorization of users within the so-called IP multimedia subsystem (IMS). The IMS is a collection of specifications of the 3GPP, with the purpose of standardizing access to services based on different network technologies. The home subscriber server therefore provides similar functions as the home location register, although these functions have been developed specifically for Internet-protocol (IP)-based networks. The home subscriber server comprises user data such as user profiles, data for user authentication and data relating to the location of the user within the network. The home subscriber server is also implemented as a central entity with a large database in the network.
The disadvantage of such central databases is obvious. On one hand, an enormous size is required for the databases, in order to store the user data of all network subscribers. This results in high hardware costs and considerable technical complexity, in order to provide the memory capacity and the high data transfer rate for simultaneous access to a plurality of user data items in the database. On the other hand, a central database involves a considerable failure risk, with the communication throughout the entire network collapsing if the database fails.
In the field of wired IP (Internet Protocol)-based networks, so-called peer-to-peer networks are known, in which all the network nodes have equal authority and are connected to one another, and in which data is stored in a correspondingly decentralized form, distributed across the network. Central entities such as databases for storage of user data can be saved in this way. When using this technology, the user data is stored in the terminals that are used for communication, that is to say the computers that are connected to the network.
So-called distributed hash tables are used to store and find data. These are used to find data elements in a large data set, by providing an index structure in the form of a table. Distributed hash tables (DHT) make it possible to distribute data objects as uniformly as possible across all the nodes, allowing routing to a specific network node, independently of the location of a certain entry point.
Consistent hash functions form the basis of distributed hash tables and are used to allocate keys in a linear value range to the data objects. In this case, the value range is distributed as uniformly as possible between the network nodes of the node quantity, with each node being responsible for at least one subspace of the key space. In the hash tables, information is stored in the form of a data pair comprising the key, also referred to as the hash value, and information associated with it. When a search is carried out for a specific data object in a peer-to-peer network, this can be done by means of distributed hash tables such that the hash function is used to calculate a hash value for the name (identifier) that identifies the data object. The hash value contains the memory location of the data object in the network, thus making it possible to search for the data object at the correct location. With the name converted to a hash value, distributed hash tables represent an efficient mechanism for storage and finding of information items associated with the hash value.